1. Field of the Invention
The present invention is generally related to apparatus for dispensing controlled amounts of fluid.
2. Description of the Related Art
Many research and/or manufacturing settings require the delivery of a precise amount of fluid. Precisely controlling the delivery of fluid can be important to producing accurate test results or to producing high quality products, as well as being important in lowering costs associated with such operations. Often, these applications require a large number of repetitive operations. For example, biological or chemical assays may employ hundreds, thousands, or more of individual testing steps. Efficiency, accuracy and repeatability require that these operations be automated. One method of automating is to perform multiple tests at discrete locations on a single plate (i.e., plate, slide, or array). This requires the delivery of very precise amounts of fluids, for example agents or reagents, to hundreds or even thousands of locations on the plate. Other automated methods are of course possible. The cost of high precision automated equipment is typically substantial.
One approach to delivery of a controlled amount of fluid employs pipette tips. The pipette tip relies on capillary action to draw a precise amount of fluid from a reservoir into an internal passage of the pipette tip, for delivery to the desired location. Pipette tips may be particularly suitable for dispensing fluids in the micro-liter range.
U.S. Pat. No. 5,497,670 issued Mar. 12, 1996 discloses a dispensing apparatus including means for loading pipette tips carried by a pipette plate onto dispensing cylinders such that a loading force is maintained during the operation to ensure a hermetic seal. The pipette tips are manually placed on the pipette tip plate, the pipette tip plate being slidingly received within the dispensing apparatus.
U.S. patent application Ser. No. 08/751,859 filed Nov. 18, 1996 discloses a dispensing apparatus. The dispensing apparatus is similar to that disclosed in the aforementioned patent, but substitutes a more conventional pipette tip carrier for the pipette tip plate, which is less expensive, less likely to be contaminated, and easily adapted for robotic operation or automation.
U.S. application Ser. No. 10/027,448 filed Dec. 20, 2001 discloses a dispensing apparatus that employs a modified pipette tip box tray carrier to furnish pipette tips carried in a standard pipette tip box to the apparatus, and includes engagement means to engage pipette tip box tray carrier such that the pipette tips are loaded into corresponding internal cylinders formed in a dispense block head of the dispensing apparatus. The dispense block head comprises a solid block of material having a plurality of internal cylinders to engage the pipette tips in a sealing engagement.
A distinctly different approach to precisely dispensing fluids employs one or more pins to retrieve a desired amount of fluid from a reservoir, and to dispense the retrieved fluid to a desired location. In contrast to pipette tips, these pins do not include an internal passage, but rather retrieve a small sample of the fluid as the pin is removed from a reservoir, the fluid forming a droplet on the outer surface at the end of the pin. The amount of fluid retrieved by the pin is a function of a number of parameters including the size, shape and material of the pin and the viscosity of the fluid, all of which affect surface tension. The pin based approach may be particularly suitable for dispensing fluids in the nano-liter range.
Automating the pin based approach would be highly desirable, as would be the taking advantage of the substantial investment made in existing automated equipment such as pipette based dispensing apparatus.